Process for the preparation of silver halide emulsions by the flocculation method



United States Patent Ofitice 3,366,482 Patented Jan. 30, 1968 3,366,482PROCESS FOR THE PREPARATION OF SILVER HALIDE EMULSIONS BY THE FLOCCULA-TION METHOD Heinrich Schaller and Walter Anderan, Fribourg, Switzerland,assignors to Ciba Limited, Basel, Switzerland, a Swiss company NoDrawing. Continuation-impart of application Ser. No. 307,376, Sept. 9,1963. This application Mar. 7, 1967, Ser. No. 621,117 Claims priority,application Switzerland, Sept. 13, 1962, 10,850/ 62 9 Claims. (CI.96-94) ABSTRACT OF THE DISCLOSURE In the process for the preparation ofphotographic silver halide emulsions the extraneous soluble saltsresulting from the reaction of silver nitrate with water-soluble halidesin an aqueous gelatine solution, are removed by flocculation of thesilver halide emulsion. The flocculation is carried out at a pH of 3 to7 and the emulsion starts to flocculate immediately on the addition ofthe flocculating agent. The flocculating agents are colorless compoundsthat contain at least one six-membered heterocyclic ring made up of 3 to4 carbon atoms, at the most one halogen atom being bound to a carbonatom of said heterocyclic ring, at least one aromatic radical, and atleast one acidic group imparting solubility in Water to the compound.Thesix-membered heterocyclic ring Which may be substituted by at themost one halogen atom, e.g. bromine, but more especially chlorine, mayalso contain other substituents, under the conditions of thisflocculating process, no gelatine derivatives are formed together withthe flocculating agents.

Photographic silver halide emulsions of all kinds, especially coloremulsions, may be prepared by this process.

Cross-reference This application is a continuation in part of applicantscopending application Serial No. 307,376, filed Septemher 9, 1963, nowabandoned the disclosure of which is relied on and incorporated byreference in this application.

Background The present invention relates to a process for thepreparation of photographic silver halide emulsions in which theextraneous soluble salts are removed by flocculation of the silverhalide.

In the preparation of photographic silver halide emulsions, awater-soluble silver salt, generally silver nitrate, is usually reactedwith Water-soluble halides in an aqueous gelatine solution. Thegelatine/silver halide emulsion thus formed contains water-soluble saltswhich are by-prodnets of the double decomposition reaction, and thesesalts have to be removed. The conventional method of removing the saltsconsists in solidifying the emulsion by cooling, comminuting it, andthen washing out the salts with cold water.

Another method, known as the flocculation method,

consists in precipitating the silver halide and the gelatine or othercolloid, separating the supernatant salt solution from the precipitate,and then dispersing the precipitate in a gelatine solution or in someother suitable layer colloid.

The flocculation method oflers a number of advantages; in particular, itmakes possible the preparation of concentrated silver halide emulsions.Various methods of flocculating silver halide emulsions have beenproposed, for example, flocculation with an inorganic salt, such as, forexample, sodium sulfate. However, a large amount of the inorganic saltis required, and the precipitate has to be removed by washing out.Organic solvents can also be used for bringing about flocculation, butthis method is expensive and the precipitates obtained are highlyvoluminous and still contain a large amount of liquid. It has also beenproposed to use the salts of heavy metals as flocculating agents.However, such salts have the disadvantage that they harden the gelatineand the precipitates are very ditficult to re-disperse. It has also beensuggested that anionic substances such as soaps be used, but in thisprocess residual soap adheres tenaciously to the coagulate and tends tocause cloudiness in the emulsion.

Other methods are based on the use of gelatine derivatives. In thepreparation of gelatine derivatives, at pH values of 8 to 11 or moreinvolving reaction times of a few minutes up to 30 minutes however, thereactive amino groups of the gelatine undergo change, thus causing achange in the photographic and colloidochemical properties of thegelatine. Moreover, gelatine derivatives can only be flocculated at alow pH value, for example, at a pH value of about 3.5. In the case ofhighly sensitive ammonia emulsions, such as are used in the preparationof X-ray films, this unavoidable depression of the pH value to about 3.5brings about a loss in sensitivity of the emulsion.

Detailed description The present invention is based on the observationthat certain heterocyclic compounds are very suitable as flocculatingagents. Accordingly, the present invention provides a process for thepreparation of photographic silver halide emulsions by the flocculationmethod, which com-prises flocculating the emulsion at a pH of 3 to 7,and using as a flocculating agent a colorless compound containing (a) Atleast one six-membered heterocyclic ring made up of 3 to 4 carbon atoms,at the most one halogen atom being bound to a carbon atom of saidheterocyclic ring;

(b) At least one aromatic radical, and

-(c) At least one acidic group imparting water-solubility to thecompound, the emulsion starting to flocculate immediately on theaddition of the flocculating agent.

The acidic group imparting solubility in Water present in a flocculatingagent according to the invention may be, for example, a carboxylic acidgroup or a sulfato group, but is preferably a sulfonic acid group. Thesaid flocculating agent must also contain at least one six-memberedheterocyclic ring that contains as ring members either 3 carbon atomsand 3 nitrogen atoms or 4 carbon atoms and 2 nitrogen atoms. Thissix-membered heterocyclic ring may be substituted by at the most onehalogen atom and/ or other substituents. Examples of suitableheterocyclic rings are the pyridazine and pyrimidine rings. Compoundsthat contain at least one 1:3:5-triazine radical are particularlysuitable.

The compound to be used as a flocculating agent in the process of thepresent invention must contain at least one aromatic radical,advantageously an aromatic radical of the benzene or naphthalene series.The aromatic radical advantageously contains at least one substituent,for example, the group imparting solubility in Water, and isadvantageously bound to the heterocyclic ring either directly or througha bridge, for example, a sulfur or oxygen atom, or preferably a nitrogenatom.

A 1:3:5-triazine compound may be substituted in, for example, each ofthe 2 and 4 positions by an aromatic radical of the kind defined. The 6position may have as a substituent a halogen atom, for example, bromine,but more especially chlorine. Examples of suitable triazine compoundsfall within the formula RiNH =N Ian-r m in which R and R' eachrepresents a benzene or naphthalene radical containing at least onesulfonic acid group and Y represents a halogen atom. The benzene ornaphthalene radical may contain another substituent, for example, -afurther sulfonic acid group, a carboxylic acid group, an alkyl groupsuch as a methyl or ethyl group, an alkoxy group such as a methoxy orethoxy group, a halogen atom such as chlorine, fluorine or bromine, or a.group of more complex structure, for example, a trifluoromethyl groupor a sulfonic acid amide group.

In general, the efificacy of the flocculating agent is enhanced byincreasing the size of the molecule. Efiicacy is further increased bythe incorporation of naphthalene radicals, such radicals advantageouslybeing 1- or 2- amino-naphthalene-mono-, dior tri-sulfonic acids, whichthus produce, for example, compounds of the formula R:NH

R's-NH in which R and R g each represents a naphthalene radicalcontaining at least one sulfonic acid group.

A process which comprises condensing a condensation product ofequimolecular proportions of cyanuric chloride and an aromaticamino-sulfonic acid, especially an aminonaphthalene disulfonic acid,with an aliphatic or aromatic diamine in a molar ratio of 1:1 results inthe formation of a fiocculating agent that contains a free amino group.It has been observed that such amino compounds are highly effective atpH values around and 6.

Theseamino compounds may also be further condensed with a suitablereactive halogen compound, for example, with a condensation product ofequimolecular proportions of cyanuric chloride and an aromatic sulfonicacid already mentioned. In such manner there are obtained, for example,flocculating agents that correspond to the formula in which R and R eachrepresents a naphthalene radical containing at least one sulfonic acidgroup, and Z represents a bridge member. Symmetrical compounds of thekind defined may also be prepared by condensing cyanuric chloride withaminonaphthalene sulfonic acids and diamines in a molar ratio of 2:2: 1,respectively.

It is also possible to join together at the amino groups tWo identicalmolecules or two difierent molecules of the above-mentioned compoundscontaining a free amino group and formed from one molecule each of anaromatic amino sulfonic acid, cyanuric chloride and a diamine, the linkbeing made through suitable bridge members. There may also be usedtriazine compounds that no longer contain a halogen atom bonded to thetriazine ring. These are obtained, for example, when the last halogenatom in compounds of the kind defined above is exchanged for H0, H N orH CO groups or substituted amino groups.

The following compounds may be used as starting materials for thepreparation of fiocculating agents having a composition given above:

l-aminobenzene-2-, -3- or -4-sulfonic acid, amino-methylbenzene sulfonicacids, amino-chlorobenzene sulfonic acids, amino-methoxybenzene sulfonicacids, 1-aminonaphthalene-4-, -5-, -6- or -7-sulfonic acid,2-aminonaphthalene-4-, -5-, -6- or -7-sulfonic acid,1-aminonaphthalene-2:5-, -2:6-, -3 28-, -4:6-, -4:7-,

-4:8-, -5 :7- or -6:8-disulfonic acid, 2-aminonaphthalene-1:7-, -3 16-,-3 27-, -4:7- or -5 Z7-disulfonic acid, but more especially,2-arninonaphthalene-4 I 8-disulfonic acid, l-aminonaphthalene-2i4:6-, -32527-, -3 :6:8- or -4:6:8-

trisulfonic acid, aliphatic diamines of the formula in which nrepresents an integer of a value not greater than 5, 1:4-diaminobenzene, 1 23-diaminobenzene-4-sulfonic acid, 1 I3-diaminobenzene-4- or -5-ca rboxylic acid, 4:4-diaminodiphenyl, 44-diaminodiphenyl-2 Z'2'-diSlllfOniC acid, 4:4-diaminodiphenyl-3:3'-dicarboxylic acid, 3 13'-dicarboxymethoxy-4:4'-diaminodiphenyl and.l Z5-diaminobenzene-3 :7-disulfonie acid.

Some of the flocculating agents in accordance with the invention may beprepared by conventional methods. The following are a number of triazinecompounds in accordance with the invention. (The triazine radical of theformula HOaIS (I31 NHL HNCH:-CH2-NHQ 1103's ('31 (J1 SOaHNHAHNCHa-CHr-NH NH I SOsH HOaS (23) B0 8 1130-? (I)CH1 SOaH NH NH Z HN IHOsS 80311 SO H Bo s HO S i SOsH I C I We a r m a Cl N C- l I -C I l Cls 1103s soln N N OCH1 13 00-- 11033 H0 8 H H H038 80 K I o\ l Cl N bk IN N Cl H0 8 SOaH o L o I I I SOsH H0 3 C1 C] HO S I S0 11 I C I H- N\ /NN\ /I 1' H f a scan HOJS The compounds given above may be used asflocculating agents in the usual manner. Depending on theirconstitution, small amounts of these agents. bring about good andimmediate flocculation at a moderately raised temperature and at pHvalues in the range of from 3 to 7. It has been observed that, in theshort time between the flocculation and any washing out operation, theflocculating agents of the invention do not chemically react withgelatine forming gelatine derivatives and do not cause hardening of thegelatine when used in the small amounts required, even when flocculationis carried out with halogen triazine compounds which are reactive.

In general, flocculation is advantageously brought about by adding anaqueous solution of the flocculating agent to the emulsion, and thenadjusting the pH value of the emulsion to the requisite value. However,it is also possible to adjust the pH value first and then :add theflocculating agent. The silver halide precipitates along with thegelatine or other colloid in the form of fine granules and settles outvery quickly. The precipitate contains only a very small amount of waterso that it is generally not necessary to wash it out further. Should itappear necessary, however, the precipitate may be washed out once orseveral times with cold water; if necessary, the pH can be adjusted to asuitable value. The pH value for flocculation, is in the range of from 3to 7, preferably 3 to 5, and the requisite amount of flocculating agent,for example, to 200% (calculated on the dry weight of the gelatine orother colloid) in the form of a dilute aqueous solution, depend not onlyon the flocculating agent itself, but also on the gelatine or othercolloid concentration of the emulsion, the salt content, and otherfactors. The temperature at which flocculation is carried out has nogreat influence; it is advantageously within the range of to C., and itshould always be such that no substantial amounts of gelatine or ofanother colloid react with the flocculating agent, in so far as thelatter contains reactive groups.

Photographic silver halide emulsions of all kinds may be prepared by theprocess of the invention, especially color materials that contain eitherdyestufi components for color development or image dyestuffs for thesilver dyestufi bleaching process.

The following examples illustrate the invention, the parts andpercentages being by weight.

EXAMPLE 1 A solution of grams of silver nitrate in 600 milliliters ofwater is added in a period of 15 minutes at 50 C. to solution of 8 gramsof gelatine, 44 grams of potassium bromide and 1 gram of potassiumiodide in 600 milliliters of water. The mixture is allowed to mature for10 minutes at 50 C. and is then cooled to 40 C. 30 milliliters of aaqueous solution of the compound of Formula 20 is then added, and the pHof the emulsion is adjusted to 4.5 to 5.0 by the addition of citricacid. The nature of the acid used has no influence on the flocculationprocess; acetic acid, hydrochloric acid, sulfuric acid or any other acidwith a sulflcient degree of acidity can also be used. The silver halideprecipitates at once along with the gelatine in the form of finelydivided granules and settles out very quickly. The supernatant saltsolution is decanted oif. A solution of 120 grams of gelatine in 1400milliliters of water and having a temperature of 40 C. is added to thegranules, and the pH value is adjusted to 7.0 by the addition of aqueoussodium hydroxide solution. The silver halide is redispersed by stirringfor to 20 minutes at 40 C., and the emulsion is allowed to mature tooptimum sensitivity in a known manner at 50 to 55 C.

Solutions of the compounds listed in the following Table I may also beused to bring about flocculation of silver halide/ gelatine emulsions bythe above method instead of a solution of the compound of Formula 20.The amounts required, concentrations and pH values are also listed. Allcompounds yield emulsions having the same photographic properties.

TABLE I Amount, ml. of

Concentration, the solution percent of the solution pH value at whichflocculation is efiected Formula N o The compound of the Formula 20 canbe prepared as follows:

18.5 parts of trichlorotriazine (cyanuric chloride) are dissolved in 40parts of acetone and precipitated in a finely divided state with 100parts of water and 100 parts of ice. 30.3 parts of2-amino-naphthalene-4:8-disulfonic acid in the form of the neutralsodium salt and dissolved in 150 parts of water are then added. Themixture is stirred for a period of from 30 to 60 minutes at 0 to 4 C.and dilute sodium carbonate solution is added until the pH value remainsconstant at 5 to 6.5. No diazotizable amino compound must be detectableat the end of this period. To this primary condensation product areadded 35 parts of 4:4-diamino-diphenyl-2:2-disulfonic acid that had beendissolved in 400 parts of water at 40 C. in the form of the sodium salt.The mixture is maintained for 1 hour at 40 C. and at a pH value of 6 to7, the pH value being adjusted with sodium carbonate or sodium boratesolution. The secondary condensation product can be obtained by saltingout (that is, by the addition of 25 parts of sodium chloride per 100parts by volume of the reaction mixture). The product is the compoundshown by the Formula 20.

This product may then be further condensed at 40 C. with the primarycondensation product described above to process the compound of theFormula 28.

The compounds of the Formulae 23 to 26 may be prepared by the abovemethod when, instead of trichlorotn'azine, equivalent proportions of2-methoXy-4:6-dichloro-l :3 :S-triazine, 3-methoxy-4z5-trichloropyridazine, 224:6 trichloropyrimidine or 4:5:6trichloropyrimidine are used.

The other triazine compounds mentioned in these examples can likewise beprepared by methods in themselves known.

EXAMPLE 2 A solution of 50 grams of silver nitrate in 450 milliliters ofwater is added during a period of 20 minutes at a temperature of 65 C.to a solution of 5 grams of gelatine, 42 grams of potassium bromide and2.2 grams of potassium iodide in 450 milliliters of Water. The mixtureis allowed to mature for 15 minutes at 65 C. and is then cooled to 45 C.20 milliliters of a 5% aqueous solution of the compound of the Formula18 are added and the pH value is adjusted to 4.5 with citric acid. Thesilver halide along with the gelatine flocculates at once in the form offine granules and settles out rapidly. After decanting the clearsupernatant solution, the silver halide is redispersed in a solution ofgrams of gelatine in milliliters of water having a pH value of 7.2, andthe emulsion is then allowed to mature to its optimum sensitivity in theconventional manner.

Solutions of the compounds listed in the following Table H may also beused in place of a solution of the compound of the Formula 18 in aprocess as described above.

TABLE II Formula Amount, ml. of Concentration, pH value at which No. thesolution percent of the flocculation is solution efiected What isclaimed is:

1. A process for the manufacture of a photographic silver halideemulsion by the flocculating method, which comprises flocculating theemulsion at a pH of 3 to 7, starting the emulsion to flocculateimmediately after the first addition of flocculating agent, using as theflocculating agent a colorless compound containing (a) at least onesix-membered heterocyclic ring made up of 3 to 4 carbon atoms, at themost one halogen atom being bound to a carbon atom of said heterocyclicring,

(b) at least one aromatic radical, and

(c) at least one acidic group imparting water-solubility to thecompound, the emulsion starting to flocculate immediately on theaddition of the flocculating agent and the adjustment of the pH to avalue of 3 to 7.

2. A process according to claim 1 for the manufacture of a photographicsilver halide emulsion by the flocculating method, which comprisesflocculating the emulsion at a pH of 3 to 7, starting the emulsion toflocculate immediately after the first addition of flocculating agent,using 11 12 as the fiocculating agent a colorless compound containing 6.A process according to claim 1 for the manufacture (a) at least onetriazine radical, at the most one haloof a photographic silver halideemulsion by the flocculatgen atom being bound to a carbon atom of saidtriing method, which comprises flocculating the emulsion at azineradical. a pH of 3 to 7 using as the flocculating agent a colorless (b)at least one aromatic radical, and compound of the formula (c) at leastone acidic group imparting water-solubil- Rz-NH HNR3 ity to the compoundand the adjustment of the pH to a value of 3 to 7. 3. A processaccording to claim 1 for the manufacture /OHN"Z NH C\ of a photographicsilver halide emulsion by the flocculat- 10 C=N N=O ing method, whichcomprises flocculating the emulsion at of 3 to startmg PmulsionflocFulate wherein R and R each represents a naphthalene radicalmediately after the first addition of flocculatmg agent, containing atleast one lfo i a id group and Z repreas the flocculating agentcolorless compound sents a bridge member, the emulsion starting tofiocculate tammg immediately on the addition of the flocculating agentand (a) at least one triazine radical, at the most one halotheadjustment of the PH to a value of 3 to p amnkbeing bound to a carbonatom of said 7. A process according to claim 1 for the manufacture azmeradlcal of a photographic silver halide emulsion by the flocculat- (b)at least one aromailc f and ing method, which comprises flocculating theemulsion at (c) at least one sulfonlc acid group and the ad usta PH of 3to 5 using as the fiocculafing agent the ment of the pH to a value of 3to 7. pound of the formula 4. A process according to claim 1 for themanufacture C1 of a photographic silver halide emulsion by theflocculating method, which comprises flocculating the emulsion at HogspH of 3 to 7 using as the flocculating agent a colorless N N compound ofthe formula H, O

' I I Rr-JTIH HOaS SOa C-N N7 \FY F the emulsion starting to flocculateimmediately on the addition of the flocculating agent and the adjustmentof 1 the pH to a value of 3 to 5.

8. A process according to claim 1 for the manufacture wherein R and R'each contains at least one sulfonic of a photographic silver halideemulsion by the flocculatacid group and represents a member selectedfrom the ing method, which comprises fiocculating the emulsion at groupconsisting of a benzene radical and a naphthalene a pH of 3 to 5 usingas the fiocculating agent the comradical and Y represents a halogen atomthe emulsion pound of the formula Cl (5 H033 r it NHC GNHOCH=CHC NH1 N Il S OaH starting to flocculate immediately on the addition of the theemulsion starting to flocculate immediately on the flocculating agentand the adjustment of the pH to a value addition of the flocculatingagent and the adjustment of of 3 to 7. the pH to a value of 3 to 5.

5. A process according to claim 1 for the manufacture 9. A processaccording to claim 1 for the manufacture of a photographic silver halideemulsion by the flocculatof a photographic silver halide emulsion by theflocculating method which comprises flocculating the emulsion at ingmethod, which comprises flocculating the emulsion at a pH of 3 to 7using as the flocculating agent a colorless a pH of 3 to 5 using as theflocculating agent the comcompound of the formula pound of the formula('31 C11 0 0 ss S a t t NHO oNHon=cHONn-o C-HN- N N SOQH EO3S S OaH Tthe emulsion starting to flocculate immediately on the ON addition ofthe flocculating agent and the adjustment of the pH to a value of 3 to5.

References Cited R'2 H 7O wherein R and R' each represents a naphthaleneradical UNITED STATES PATENTS containing at least one sulfonic acidgroup, the emulsion 3,138,461 6/1964 Ryan 96-94 starting to flocculateimmediately on the addition of the 3,288,775 11/1966 Anderau et al 961l1u i g ag t and the adjustment of the pH to a value of 3 to 7. J. TRAVISBROWN, Acting Primary Examiner.

